摘要:

AbstractEnzymes deposited on solid support usually show good stability when operated in organic solvents. Decreased stability of the enzyme preparations was noticed when low enzyme loadings were used (e.g., with Celite as support; less than 1 mg enzyme/g). It was possible to avoid the activity loss by the addition of an additive which protects the enzyme during the immobilization. Proteins (such as albumin, gelatin, and casein) and poly(ethylene glycol) were effective additives whereas amino acids, monomeric carbohydrates, and polysaccharides had no effect. The amount of additive needed for stabilization was shown to depend on the structure of the support, more additive being required for a support with high porosity. The stabilizing effect was investigated in a series of glyceryl‐controlled‐pore glass (CPG) with varying specific surface areas (9.5–180 m2/g). The minimum addition of albumin, giving full stabilization, on the different supports correlated to a monolayer coverage of the surface, approximately 2–3 mg protein/m2. The effect of the additive was less pronounced when increasing amounts of enzyme were immobilized (5–40 mg enzyme/g Celite). The effect of the additives was studied using mandelonitrile lyase, but α‐chymotrypsin and lipase P were also shown to be stabilized. © 1993 John Wi

ISSN:0006-3592    

DOI:10.1002/bit.260410202

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractRecombinant human kidney epithelial 293 cells were cultivated as aggregates in suspension. The concentration calcium ion, in the range of 100 μM to 1mM, affected the rate of aggregate formation. During the course of cultivation the size distribution of aggregates shifted and the fraction of larger aggregates increased. This effect was more profound in cultures with a high calcium concentration. Scanning and transmission microscopic examination of the aggregates revealed that cell packing was greater in the high calcium cultures and that ultrastructural integrity was retained in aggregates from both low and high calcium cultures. Confocal microscopy was applied to examine the viability of cells in the interior of the aggregates. High viability was observed in the aggregates obtained from exponentially growing cultures. Aggregates from the high calcium culture in the stationary phase exhibited lower viability in the interior. With its ease of retention in a perfusion bioreactor, aggregate cultures offer an alternative choice for large‐scale operation. © 1993 John Wiley&Sons,

ISSN:0006-3592    

DOI:10.1002/bit.260410203

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThe influence of cell‐cell adhesion on the growth behavior of Chinese hamster ovary (CHO) cells in suspension culture was investigated. CHO cells form aggregates under suboptimal growth conditions. Clusters are formed around decaying and dead cells. The deoxyribonucleic acid (DNA) released from these cells was found to mediate the cells was found to mediate the cell‐cell adhesion. Cluster formation dramatically influenced the growth behavior of the cells. First, cells within aggregates showed a strongly reduced specific proliferation rate, and second, shear forces exerted on large aggregates caused a considerable higher specific death rate than those exerted on single cells. These factors led to a reduction of the specific growth rate up to 50%. This decrease could be avoided by addition of DNase 1 to the medium. It is shown that the separate determination of the specific proliferation and death rates is not feasible with state‐of‐the‐art methods. To achieve a more profound and precise description of the growth pattern of animal cells, we propose an extended Monod model and describe the relevant methods. © 1993 John Wiley

ISSN:0006-3592    

DOI:10.1002/bit.260410204

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractWe have developed a hepatocyte entrapment hollow fiber bioreactor for potential use as a bioartificial liver. Hepatocytes were entrapped in collagen gel inside the lumen of the hollow fibers. Medium was perfused through the intraluminal region after contraction of the hepatocyte‐entrapment gel. Another medium stream, comparable to the patient's blood during clinical application, passed through the extracapillary space. Viability of hepatocytes remained high after 5 days as judged by the rate of oxygen uptake and viability staining. Urea and albumin synthetic activities were also sustained. Transmission electron microscopic examination demonstrated normal ultrastructural integrity of hepatocytes in such a bioreactor. With its sort‐term, extracorporeal support of acute liver failure, the current bioreactor warrants further investigation. © 1993 John Wiley&Sons,

ISSN:0006-3592    

DOI:10.1002/bit.260410205

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractIn order to investigate quantitatively the interesterification reaction, triolein and stearic acid were used as substrates and eight commercially available lipases were tested for their suitability for the reaction. Three fungal lipase preparations were found to be suitable. The hydrolytic activity of the commercial lipases was tested with olive oil, and it 2was noted that there was no correlation between their hydrolytic and interesterification activities. Among the lipases tested,Mucor mieheilipase was chosen for further study because of it high protein content and its relatively high hydrolytic and interesterification activities, both of which are required for effective interesterification. The effect of water activity of the interesterification reaction was investigated. interesterification activity was shown to be maximum at the water activity of 0.25. As the water activity of the lipase increased, hydrolysis of triglyceride was accelerated. At zero water activity, high conversion was achieved, although interesterification activity was relatively lower than that at the water activity of 0.25. A new and simple immobilization method was developed in order to render hydrophobicity to the lipase and hence to improve the interesterification activity of the lipase. The lipase was immobilized covalently with glutaraldehyde or with six alkyl chains as spacers onto Florisil (magnesium silicate, a inorganic matrix). Interesterification activity of the immobilized lipase with the hydrophobic spacers were increased against that of re lipase. The increase of activity was up to 8‐fold that of the original activity of free lipase when the spacer was 7‐aminoheptanoic acids. Relatively high stability of the immobilized lipase was shown in a continuous packed bed column reactor with a half‐life of 97 days. © 1993 John Wiley&Son

ISSN:0006-3592    

DOI:10.1002/bit.260410206

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractDifferences in plasmid retention and expression are studied in both suspended and biofilm cultures ofEscherichia coliDH5α(PMJR1750). An alternative mathematical model is proposed which allows the determination of plasmid loss probability in both suspended batch and continuously fed biofilm cultures. In our experiments, the average probability of plasmid loss ofE. coliDH5α(pMJR1750) is 0.0022 in batch culture in the absence of antibiotic selection pressure and inducer. Under the induction of 0.17 MMIPTG, the maximum growth rate of plasmid‐bearing cells in suspended batch culture dropped from 0.45 h−1to 0.35 h−1and the β‐galactosidase concentration reached an experimental maximum of 0.32. pg/cell 4 hours after the initiation of induction. At both 0.34 and 0.51 mMIPTG, growth rates in batch cultures decreased to 0.16 h−1, about 36% of that without IPTG, and the β‐galactosidase concentration reached an experimental maximum of 0.47 pg/cell 3 hours after induction.In biofilm cultures, both plasmid‐bearing and plasmid‐free cells in increase with time reaching a plateau after 96 hours n the absence of both the inducer and any antibiotic selection pressure. Average probability of plasmid loss for biofilm‐boundE. coliDH5β(pMJR1750) population was 0.017 without antibiotic selection. Once the inducer IPTG was added, the concentration of plasmid‐bearing cells in biofilm dropped dramatically while plasmid‐free cell numbers maintained unaffected. The β‐galactosidase concentration reached a maximum in all biofilm experiments 24 hours after induction; they were 0.08, 0.1, and 0.12 pg/cel under 0.17, 0.34, and 0.51 mMIPTG, respectively

ISSN:0006-3592    

DOI:10.1002/bit.260410207

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractAn optimized, defined minimal medium was developed to support balanced growth ofEscherichia coliX90 harboring a recombinant plasmid. Foreign protein expression was repressed in these studies. A pulse injection technique was used to identify the growth responses to nutrients in a chemostat. Once the nutrients essential for growth had been identified, the yield coefficients for individual medium components. These yield coefficients were used to develop an optimized, glucose‐limited defined minimal medium that supports balanced cell growth in chemostat culture. The biomass and substrate concentrations follow the Monod chemostat model. The maximum specific growth rate determined in a washout experiment is 0.87 h−1for this strain in the optimized medium. the glucose yield factor is 0.42 g DCW/g glucose and the maintenance coefficient is zero in the glucose‐limited chemostat culture. © 1993 John Wiley&Son

ISSN:0006-3592    

DOI:10.1002/bit.260410208

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThe quasi‐steady behavior of a continuous flow reactor in which hydrogen peroxide is decomposed by immobilized catalase is investigated. Under certain conditions, reactors involving such substrate‐inhibited, self‐poisoning reactions are susceptible to suddne failure and the reactor moves catastrophically from high‐ to low‐conversion quasi‐steady states. This exchange‐of‐steady‐states phenomenon is ex‐amined in the light of experimental evidence for the enzyme catalase from bovine liver. © 1993

ISSN:0006-3592    

DOI:10.1002/bit.260410209

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThe article describes four different fermentation procedures forEscherichia coliAN311, a producer of enterobactin. A regular rotary shaker culture with a biphasic system consisting of an agar layer (as a reservoir for feeding processes) and a layer of liquid medium, 2.4 L and 10 L batch cultures, and a novel dialysis membrane fermentor were used. With the use of this latter fermentor type, the production of enterobactin could be increased by a factor of about 9.5, while growth increased by a factor of 12 compared to the other systems. For the rapid and reliable quantification of the concentration and purity of enterobactin an analytical and preparative high‐performance liquid chromatography (HPLC) method was established. The degradation compounds of this siderophore were detected by diodearray and bioassays. A comparison of total catechol production as well as the distribution between enterobactin and its degradation compounds is given. © 1993 John Wiley&Sons, I

ISSN:0006-3592    

DOI:10.1002/bit.260410210

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractAn in vitro silk fibroin production system has been developed by culture of posterior silk glands fromBombyx mori.A large amount of the silk fibroin was produced continuously and effectively with a rotation culture procedure. Modified Grace's insect medium was used, and oxygen bubbling in the medium was performed. In addition, half of the medium was replaced with fresh medium every 6 h. The production yield of silk fibroin produced after 100 h culture was 81 mg/g wet weight of posterior silk gland. This culture system was used successfully for efficient15N isotope labeling of silk fibroin, which is required for15N solid state nuclear magnetic resonance (NMR) analysis of silk fibroin. Moreover, the introduction of fluorinated amino acids into silk fibroin was also carried out using this culture system. © 1993 John Wiley&Sons, Inc

ISSN:0006-3592    

DOI:10.1002/bit.260410211

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY